North Korea has fired an unidentified projectile off its east coast, South Korea's military said, in what is likely the latest test-launch of an intercontinental ballistic missile (ICBM).

Key points:

The projectile flew for six minutes before crashing into the Sea of Japan

No damage to planes or ships has been detected, officials say

Japan vows action to deter Pyongyang's repeated provocations

The statement by the Joint Chiefs of Staff early Monday morning did not say what type of projectile was fired or if it was successful.

South Korea's Yonhap news agency, without citing a source, said the projectile is believed to be a ballistic missile, but the South Korean military said it was still analysing what exactly the North launched.

US authorities tracked the six-minute flight until it crashed into the Sea of Japan, the US Pacific Command said.

"We continue to monitor North Korea's actions closely," it said, adding it was working on a more detailed assessment of the launch from near the country's Wonsan Airfield.

"US Pacific Command stands behind our ironclad commitment to the security of our allies in the Republic of Korea and Japan.

"The North American Aerospace Defence Command (NORAD) assessed that the missile launch from North Korea did not pose a threat to North America."

Japan's Prime Minister Shinzo Abe condemned the launch and vowed action along with other nations to deter Pyongyang's repeated provocations.

"As we agreed at the recent G7, the issue of North Korea is a top priority for the international community," Mr Abe told reporters in brief televised remarks.

"Working with the United States, we will take specific action to deter North Korea."

"Japan absolutely cannot tolerate North Korea's repeated provocative actions. We have strongly protested to North Korea and condemn its actions in the strongest terms," said Japan's Chief Cabinet Secretary Yoshihide Suga.

Mr Suga said no damage to planes or ships had been detected.

Each test puts North Korea closer to missile goal

North Korea has increased its test-firing of ballistic missiles over recent months as it seeks to build nuclear-tipped missiles that can reach the US mainland.

It is still thought to be several years away from this goal, but each new test puts it closer to success.

The North's nuclear and missile programs are perhaps the biggest foreign policy challenges to the new leaders in allies Washington and Seoul.

Besides its regular ballistic missile test-launches, the North carried out two nuclear tests last year — in January and September.

US President Donald Trump's public statements have alternated between confrontational and flattery. But his administration is still working to solidify a policy to deal with North Korea's nuclear ambitions.

A new liberal president in Seoul, Moon Jae-in, has signalled he will be flexible in expanding civilian exchange with North Korea.

But many analysts say Mr Moon will not likely push for any major rapprochement projects because North Korea has gone too far on its nuclear program.

Outside analysts believe North Korea may be able to arm some of its shorter-range missiles with nuclear warheads, though the exact state of the North's secretive weapons program is unknown.

Mr Moon has made tentative steps toward engaging the North by restarting stalled civilian aid and exchange programs as a way to improve strained ties.

South Korea said recently that it will allow a civic group to contact North Korea about potentially offering help in treating malaria, the first government approval on cross-border civilian exchanges since January 2016.

Moscow's words and actions — including the alleged poisoning of a former spy — are not the results of random aggression but rather fall into distinct patterns that can help us anticipate Russia's next moves under Vladimir Putin.